104 



HISTOLOGY 



a cuticular border and gives rise to a tapering projection known as Tomes's 

 process. Tomes's processes extend into the developing enamel, but 

 they may readily be seen in specimens in which the layer of ameloblasts 

 has shrunken away from the enamel, as in Fig. 93. Around these proc- 

 esses minute globules are deposited, which resemble the granules within 

 the cells, since they blacken with osmic acid. They are described as 

 composed of a horny substance similar to that found in the epidermis. 

 This material may become fibrillar, and Tomes's processes also readily 

 break up into fibrils. There is therefore an uncalcified fibrillar layer of 



Cuticular 

 border. 



Tomes's Enamel 

 processes, cement. Calcified, . . uncalcified dentine. 



Enamel pulp. 

 Outer enamel cells. 



Odontoblasts. Pulp. 

 Inner enamel cells 



(ameloblasts) . 



FIG. 93. PORTION OF A LONGITUDINAL SECTION OF AN INCISOR TOOTH FROM A NEWBORN KITTEN. 

 In this section the Tomes's processes have shrunken away from the enamel cement. 



Rectangle enclosing the portion 

 of the tooth shown highly magni- 

 fied in the adjoining part of the 

 figure. 



X 300. 



enamel next to the ameloblasts. Further from the ameloblasts the 

 enamel is calcified and consists of rods known as enamel prisms (sometimes 

 called enamel fibers) which are bound together by calcified matrix or 

 enamel cement. The way in which the prisms develop has not been fully 

 determined. They have been regarded as the calcified ends of the 

 ameloblasts and also as intercellular deposits. 



The formation of enamel begins at the tof>> of the crown of each tooth 

 and spreads downward over its sides. If the tooth has several cusps, a 

 cap of enamel forms over each, and these caps later coalesce. The enamel 

 increases in thickness by the elongation of the prisms, which extend 

 across it from the inner to the outer surface. 



